1. Field of Invention
The present invention relates generally to the deposition of soluble materials and more particularly to the deposition of soluble materials using ink-jet technology.
2. Description of Related Art
Herein the expression xe2x80x9csolid surfacexe2x80x9d is used to mean the surface of a material which does not exhibit a capillary force. Fibrous materials, including paper, exhibit a capillary force and this is used as an essential part of the process for printing on such materials, such as the printing of inks on paper.
In recent years there has been an increase in the number of products which require, as part of their fabrication process, the deposition of soluble materials such as polymers, dyes, a colloid materials and the like on solid surfaces. One example of these products is an electroluminescent display device. An electroluminescent display device requires the deposition of soluble polymers on to a solid substrate. The substrate may, for example, be formed of glass, plastics or of silicon.
In the manufacture of semiconductor display devices it has been conventional to use photolithographic techniques. However, photo-lithographic techniques are relatively complex, time consuming and costly to implement. In addition, photo-lithographic techniques are not readily suitable for use in the deposition of soluble materials. This has hindered the development of products such as electroluminescent display devices. Consequently, it is proposed to use ink-jet technology to deposit soluble materials, such as depositing polymers in the fabrication of electroluminescent display devices.
Ink-jet technology is, by definition, ideally suited to the deposition of soluble materials. It is a fast and inexpensive technique to use. It instantly provides patterning, in contrast to techniques such as spin coating. However, deposition of soluble materials on solid surfaces using ink-jet technology differs from the conventional use of that technology, to deposit ink on paper, and a number of difficulties are encountered. In particular, the specific properties of the soluble materials it is desired to use often differ significantly from the properties of ink used for conventional printing. Also, as already mentioned, the capillary force inherent in a material such as paper plays a significant part in the ink printing process and this aspect of the process is absent when dealing with deposition on to a solid surface.
When depositing soluble materials on a solid surface one of the main requirements is to achieve a homogeneous layer, especially where the solution to be deposited contains two or more different components. It is also a non-trivial problem to obtain the desired thickness of the deposited layer. Issues such as homogeneousness and layer thickness are-not crucial when printing ink on paper but are crucial for the fabrication of devices such as electroluminescent displays, particularly given the desire for uniform light output, uniform electrical characteristics and the spatial limitations often imposed in device fabrication. In device fabrication there is a need to minimise the difference in morphology and properties between parts of the device. Generally, these requirements have not been met prior to the present invention and the use of ink-jet technology for the deposition of soluble materials on solid surfaces has thus not previously been implemented on a practicable basis.
According to a first aspect of the present invention there is provided a method of depositing a soluble material on a substrate comprising the steps of: loading the soluble material into an ink-jet print head; providing a flow of gas between the ink-jet print head and the substrate or adjacent thereto; and ejecting the material from the print head so as to deposit it on the substrate.
According to a second aspect of the present invention there is provided an apparatus for depositing a soluble material on a substrate, comprising an ink-jet print head and gas flow means for providing a flow of gas between the ink-jet print head and the substrate or adjacent thereto.
In a preferred arrangement, heating of the substrate during deposition is also provided. In a most preferred arrangement, the deposition is additionally conducted on the basis of continuous formation of a sequence of partially overlapping dots.